The present disclosure relates to vehicle drive systems. More particularly, the present disclosure relates to hybrid vehicle drive systems employing electric and hydraulic components.
Hybrid vehicle drive systems can employ at least two prime movers arranged in different configurations relative to a transmission. One known configuration is found in so-called “series-parallel” hybrids. “Series-parallel” hybrids are arranged such that multiple prime movers can power the drive shaft alone or in conjunction with one another.
A hybrid vehicle drive system can include a first and second prime mover (e.g., an internal combustion engine and an electric motor/generator) arranged in a parallel configuration and used to provide power to a drive shaft and a power take-off (PTO) shaft through a transmission. PTO shafts are generally used to drive auxiliary systems, accessories, or other machinery (e.g., pumps, mixers, barrels, winches, blowers, etc.). One limitation of this system is that the second prime mover is typically positioned between the first prime mover and the transmission, creating the need to reposition existing drive train components.
A hybrid vehicle drive system can also include a first prime mover (e.g., an internal combustion engine) that drives a PTO through a transmission. A second prime mover (e.g., electric motor/generator) can be coupled directly to the PTO. The applications incorporated herein by reference have described hybrid drive systems that also include an accessory such as a fluid motor/pump. Space required for the electric motor and hydraulic motor/pump can be limited. In addition, shafts, linkages, and couplings for attaching the fluid pumps/motor, the electric motor/generator, and the PTO can take additional space and require clearance that affects the placement of other vehicle components.
A hybrid system can also include a PTO mounted to a transmission that is coupled to a through shaft electric motor that is coupled to an end mount hydraulic motor. A hybrid system can also include a PTO mounted to a transmission that is coupled to an accessory with a through shaft. The accessory can be a hydraulic pump. The accessory is coupled to an end mount electric motor. One disadvantage of both designs described above is the need for a component with a through shaft. Electric motors with a through shaft are typically more difficult to procure, and when directly coupled to a PTO, often rotate at a speed relatively close to that of the first prime mover. The speed of rotation of the first prime mover is often not at the speed of rotation needed by an electric motor for optimal efficiency.
Another disadvantage of using an electric motor with a through shaft occurs if the motor is a permanent magnet electric machine and there is a fault in the hybrid system, such as a short or open circuit. In such situation, the electric motor may not be able to be rotated due to the existence of an electrical shock hazard, causing the accessory coupled to the electric motor to be completely inoperative. In the case of the hydraulic pump with a through shaft, it is often very difficult to install the hybrid drive system unless a functioning hydraulic system is installed at the same time, since the hydraulic pump must rotate to couple the electric motor to the transmission through the PTO. Rotating a hydraulic pump without fluid may cause severe damage to the pump. Mounting the hydraulic pump in between the electric motor and the PTO also causes the system to rotate the pump even if hydraulic flow is not needed by equipment, typically creating unwanted parasitic energy losses for the hybrid system. To minimize parasitic losses, a pump or hydraulic system may have to be modified so that the hydraulic pump can be uncoupled from the transmission during driving of the vehicle, causing additional expense.
Therefore, a need exists for hybrid system or vehicle idle reduction system in which the electric motor can be installed before the accessory is installed, that can accept a more common end mount electric motor, that can allow the electric motor to rotate at a significantly higher speed than the first prime mover, that is modular and easy to install, that can be installed external to the transmission, that can optionally uncouple the accessory when it is not needed, that allows for lower cost accessories to be utilized, while still providing propulsion, and that can rotate the accessory and uncouple the electric motor, if the electric motor has a fault. Also, a need exists for a hybrid vehicle drive system and method of operating a hybrid vehicle drive system that allows a drive shaft to receive power from at least three components. There is also a need for a hybrid vehicle drive system that allows for the prevention of friction and wear by disengaging unused components. There is also a need to overcome disadvantages associated with a split shaft PTO used from a drive axle, including stationary only use, locked wheels, and the need to connect with another PTO instead of the drive shaft to the wheels. There is a further need for a hybrid vehicle drive system that uses a compact structure including a PTO, electric motor, and a fluid pump. Still further, there is a need for a PTO-based hybrid system that can be easily retrofitted and includes a fluid pump/motor and an electric motor/generator. Further still, there is a need for a hybrid PTO system with a fluid pump/motor and electric motor/generator optimized for use with a vehicle, such as a boom truck.